There are several types of multiline telephone systems on the market today. One type of multiline system is referred to as a “key telephone system.” This type of system has multiple telephones known as “key telephones”, each connected by a communication medium to a central control box referred to as a “key service unit” (KSU).
There are some potential problems with a key telephone system. One problem is the wiring required for each telephone in the system to be connected to the central control box. Another problem is that since most of the intelligence is built into the central control box, there is a single point of failure in the system.
A KSU-less multiline telephone system, on the other hand, does not require a key service unit. The telephones in the system are simply interconnected to each other. The intelligence is distributed among the individual telephones, instead of being centralized in a KSU. A KSU-less system may, therefore, be more desirable, especially in a small business or home office environment.